Problem Solvers Air-Bob Universal Tire Inflator
If you have an air compressor in your shop and change a lot of bicycle tires you want the Air Bob. This is a shop-quality tire inflator with a gauge, bleed valve and a smart head for presta and schrader valves, with a thumb lock.
The Air-Bob is very easy to use and works extremely well.
I bought mine (at full price) from notubes.com, though any LBS with a QBP account can get it.
About $90 retail.